1. Field of the Invention
The present invention relates generally to a web-feed mechanism adapted for a rotary printing machine, and more particularly to a tension control device for stabilizing the tension applied to paper web fed from one of web-feed sections, which section is equipped with a specially designed brake system to feed continuously paper web from another web-feed section at the time when remaining roll of the previously working web-feed section reaches to a predetermined level.
2. Description of the Prior Art
Conventional tension control devices for stabilizing the tension applied to a paper web during a working state of a rotary printing machine have been disclosed in some publications such as Tokkosho 61-44786 (Japanese Patent Publication No. 44786/1986), referred to First Prior Art, and Tokkohei 5-45501 (Japanese Patent Publication No. 45501/1993), referred to Second Prior Art.
The tension control device according to the First Prior Art is associated with a paper feeding system which picks up a paper web from a web-feed section supported by a supporting section including a brake mechanism and feeds the web toward a printing section via guide rollers and floating roller(s). The floating roller is supported by an arm through a pivot, and a tension sensor is mounted on the pivot of the arm and connected to three different pneumatic systems. In detail, a first pneumatic system is actuated during a normal running stage, a second pneumatic system is actuated during a paper splicing stage, and a third pneumatic system is actuated during any emergencies. The first pneumatic system adjusts pneumatic pressure to be fed into the brake mechanism in response to the tension level detected by the sensor, and thus the brake mechanism comes into braking effect upon rotating motion of the web-feed section. The second pneumatic system includes a high pressure pneumatic reservoir which can store a predetermined high level of pneumatic pressure via a high pressure pneumatic valve for setting such predetermined high level pneumatic pressure, and feeds the same level pneumatic pressure as the predetermined high level pneumatic pressure into the brake mechanism through a booster relay in response to a signal from a cutter which works during a paper splicing stage. The third pneumatic system includes another high pressure pneumatic reservoir which can store predetermined high level of pneumatic pressure via an emergency stop control valve, and feeds in response to an emergency stop signal the same level pneumatic pressure as the predetermined high level pneumatic pressure stored in the reservoir into the brake mechanism through the booster relay. Thus one of these three pneumatic systems is automatically actuated and always applies a stable tension to the paper web fed from one of web-feeds toward the printing section.
The tension control device according to the Second Prior Art comprises a paper feeding means accompanying with a brake mechanism for braking the feeding motion of a web-feed, a tension sensor for detecting the tension level of the paper web fed from the web-feed, and a suppositive tension applying means for applying a suppositive tension to the tension sensor. The suppositive tension applying means applies such suppositive tension to the tension sensor during a paper leading operation and then the brake mechanism is actuated, so that the paper web leading from web-feed toward a printing section can be applied with the optimum tension.
Since the tension control device shown in the First Prior Art needs a plurality of pneumatic reservoirs, booster relay, double using of shuttle valves, and so on, such components configure a complicated pneumatic circuit which cannot quickly control the tension to be applied to the paper web. Further, during the paper leading operation prior to printing, the device shown in the First Prior Art must become temporarily ineffective to allow an operator to adjust the feeding speed of the paper web manually. This manual adjusting work reduces the efficiency of the whole of printing system.
Since the tension control device shown in the Second Prior Art includes a single pneumatic circuit for tension control which is commonly used for both normal working and paper splicing stages, the tension control cannot be effectively performed and thus the feeding tension after the paper splicing stage tends to fluctuate remarkably. This may cause various troubles such as loosening and breaking in running paper web. Further, since this second device uses means for applying a suppositive tension directly to a tension sensor, this applied suppositive tension must be gradually released from the tension sensor during paper web running operation after completion of paper leading operation in order to return the tension sensor to its normal detecting mode capable of detecting the actual tension applied to the running paper web. This transition is not a short period, so that the paper web fed within this transition may cause a great deal of spoilage. The device according to Second Prior Art should be improved in working efficiency to reduce a waste paper.